This invention relates to a dynamic electromechanical orthotic or prosthetic device with a wrap spring clutch.
Many amputees and patients with partial or complete paralysis of the extremities require assistive technology such as, for example, prostheses or orthoses, respectively (referred to herein by the general term orthosis or orthotic device), to enhance mobility.
For example, to function efficiently, the lower extremity should have the ability to: (1) support body weight during the stance phase of the locomotion cycle (when the foot is in contact with the ground); (2) rotate and coordinate the joints to achieve forward progression; (3) adjust limb length by flexing the knee during the swing phase of gait (when the foot is not in contact with the ground); and (4) further smooth the trajectory of the center of gravity by slightly flexing the knee in mid-stance.
To provide efficient locomotion, a knee-ankle-foot orthotic (KAFO) must restrain knee joint flexion at heel strike through the stance phase of the gait while also permitting free knee flexion during the gait swing phase. KAFOs with electromechanical knee restraint components utilize a wide variety of electronically controlled mechanical clutch and brake designs to provide knee control during walking. One successful design includes a small, lightweight, electronically controlled knee lock mechanism that can be installed on a conventional KAFO. Referring to FIG. 1, the KAFO device 10 includes an orthotic with an upper portion 12 with a thigh cuff 14 and thigh retaining straps 16, as well as a lower portion 18 with a lower leg/foot cuff 20 and corresponding foot retaining straps 22. A medial thigh strut 24 and a medial shank strut 26 are connected by a conventional hinge 28 at the knee joint on the medial side of the device 10. On the lateral side of the device, a lateral thigh strut 30 connects to the thigh cuff 14 and extends outwardly at a bend 32 to engage the output hub 38 of a knee hinge clutch mechanism 34. The input hub 36 of the clutch mechanism 34 is connected to a generally straight lateral shank strut 40 joined to the lower leg/foot cuff 20.
Referring to FIG. 2, the clutch mechanism 34 is a wrap spring clutch. Wrap spring clutches are a known class of overrunning clutches that allow torque to be transmitted from one shaft to another in only one direction of rotation. The clutch mechanism 34 includes a cylindrical input arbor 42 attached to the input hub 36, a cylindrical output arbor 44 attached to the output hub 38, and a cylindrical spring 46 having turns with a substantially square cross sectional shape. The input arbor 42 and the output arbor 44 are the same diameter and maintained end-to-end in an abutting relationship by a retaining clip (not shown), and rotate on a common axis. This rotational axis, referred to herein as the flexion extension axis 48, is collinear with respect with the rotational axis of the medial hinge 28 (See FIG. 1). The spring 46 is connected to the output arbor 44, slips on the input arbor 42 and acts as self-engaging brake between them. If a torque is applied to the input hub 36 in the direction of arrow A, the spring 46 wraps down tightly onto the shaft formed by the abutting input arbor 42 and the output arbor 44, which locks the input arbor 42 and the output arbor 44 together and locks the lateral electromechanical knee joint. Conversely, when torque is applied in a direction opposite arrow A, the spring 46 unwraps from the shaft formed by the input arbor 42 and the output arbor 44, which permits the shaft to slip easily in the opposite direction and allows the electromechanical knee joint to swing freely. If the input arbor 42 and the output arbor 44 are under load and must be disengaged, a control tang 50 on the spring 46 may be moved in the direction of arrow B to release the spring 46.
Referring again to FIG. 1, a circumferential control collar 52 around the spring 46 engages the control tang 50. The control collar 52 is engaged via a turnbuckle 54 attached to the output member of an electrically actuated linear solenoid 56 mounted on the lateral thigh strut 32. The linear solenoid 56 is controlled by an electronic control system 58 attached to the belt of the wearer. The control system 58 receives electrical input signals from an arrangement of two sets of foot contact sensors and, based on these signals, generates electrical output signals to control the solenoid 56. The first set of sensors 60, 62 are force sensitive resistors mounted on the underside of the lower leg/foot cradle 20, and provide varying electrical input signals to the control module 58 dependent on the degree of contact between the cradle 20 and a walking surface. The second sensors are attached on the underside of the wearer""s opposite foot (not shown in FIG. 1) and provide varying electrical input signals to the control module 58 dependent on the degree of contact between the opposite foot and the ground. A combination logic network in the electronic control module 58 monitors electrical output commands based on the inputs from the foot sensors on the orthotic and the opposite foot. Based on the input from the sensors, a controller algorithm generates an actuation signal that is sent to the solenoid 56 for release of the clutch mechanism 34 during the swing phase of the gait.
The prosthetic/orthotic device 10 shown in FIGS. 1-2 provides an articulated knee joint system that reduces metabolic energy requirements during gait. The locking action of the clutch 34 provides knee stability during stance while allowing free knee motion during the swing phase of gait.
The orthotic device illustrated in FIGS. 1-2 provides significantly enhanced performance compared to a conventional fixed knee orthosis. However, the extremely wide lateral profile of the clutch 34 makes the device 10 unattractive and difficult to wear under clothing such as trousers or skirts. In addition, the offset between the lateral thigh strut 30 and the lateral shank strut 40 increases torsional loading at the joint compared to conventional in-line braces. The foot sensors attached to both the device 10 and the opposed foot of the wearer are both unattractive and inconvenient to connect/disconnect.
The invention provides a wrap spring clutch with a significantly reduced lateral profile, which makes an orthotic device using the clutch much more attractive to wear under clothing. The reduced lateral profile and adjacent input/output frames of the clutch also reduce torsion in the lateral knee joint region. The wrap spring clutch provides bidirectional rotation, multiple locking positions, self-engagement and simple disengagement under load with very little energy input from a power source such as a battery. The wrap spring clutch design also provides a fail-safe locking mechanism if power fails. The low profile clutch design makes the device easy to use, and, consequently, more patients requiring the assistance of an orthotic device would be more likely to actually wear it on a daily basis. The unilateral input from sensors on the orthotic device renders unnecessary the extra set of wires and sensors that previously encumbered the wearer""s contralateral foot, and also greatly simplifies attachment and removal of the device.
In one aspect, the invention is a clutch including an output hub on an output frame, and an input shaft on an input frame, wherein the input shaft rotates within a bore in the output hub. An input hub is attached on an end of the input shaft, and a spring engages the input hub and the output hub. A circumferential spring clamp secures the spring to the input hub such that the input frame and the output frame are adjacent to one another on a side of the clutch opposite the input hub.
In another aspect, the invention is an orthotic joint control apparatus, including a clutch with an output hub on an output frame and an input shaft on an input frame, wherein the input shaft rotates within a bore in the output hub. An input hub is attached on an end of the input shaft, a spring engaging the input hub and the output hub, and a circumferential spring clamp secures the spring to the input hub. The input frame and the output frame are adjacent one another on a side of the clutch opposite the input hub. A first strut is attached to the input frame a second strut is attached to the output frame.
In a third aspect, the invention is a knee-ankle-foot orthotic device, including:
(a) a medial thigh strut and a medial shank strut, wherein the medial thigh strut and the medial shank strut are attached at a hinge rotating about a flexion extension axis;
(b) a lateral thigh strut and a lateral shank strut, wherein the lateral thigh strut and the lateral shank strut are attached to a wrap spring clutch rotating about the flexion extension axis;
(c) a first orthotic member adapted to engage the thigh, wherein a medial side of the first orthotic member is attached to the medial thigh strut and a lateral side of the first orthotic member is attached to the lateral thigh strut;
(d) a second orthotic member adapted to engage at least one of the lower limb and foot, wherein a medial side of the second orthotic member is attached to the medial shank strut and a lateral side of the second orthotic member is attached to the lateral shank strut;
(e) an electrically actuated device attached to one of the first and second lateral struts, wherein said electrically activated device, when activated, disengages the clutch;
(f) contact sensors attached to an underside of the second orthotic member and acted upon by a walking surface, wherein the contact sensors generate an electrical signal corresponding to the degree of contact between the second orthotic member and the surface;
(g) a kinematic sensor generating an electrical signal based on the relative position and/or movement of the input frame with respect to the output frame; and
(h) electronic circuitry receiving electrical input signals from the contact sensors and the kinematic sensors, and generate electrical output signals to actuate the electrically actuated device.
In a fourth aspect, the invention is a process for electromechanically controlling the knee joint, including:
(a) providing a prosthetic device comprising a thigh strut and a shank strut, wherein the thigh strut and the shank strut are attached to a wrap spring clutch rotating about a flexion extension axis; a first prosthetic member adapted to engage the thigh, wherein the first prosthetic member is attached to the thigh strut, and a second prosthetic member attached to the shank strut; and
activating the clutch using electrical input signals generated by at least one contact sensor on the second prosthetic member and electrical input signals generated by a kinematic sensor corresponding to the relative position and/or movement of the first and second prosthetic members.
In a fifth aspect, the invention is a process for electromechanically controlling a knee joint in an orthotic device, including:
(a) providing an orthotic device comprising a thigh strut and a shank strut, wherein the lateral thigh strut and the lateral shank strut are attached to a wrap spring clutch rotating about a flexion extension axis; a first orthotic member adapted to engage the thigh, wherein the first orthotic member is attached to the thigh strut, and a second orthotic member adapted to engage at least one of the lower limb and foot, wherein a the second orthotic member is attached to the shank strut; and
activating the clutch using electrical input signals generated by at least one contact sensor on the second orthotic member and electrical input signals generated by a kinematic sensor corresponding to the relative position and/or movement of the first and second orthotic members.
In a sixth aspect, the invention is a process for electromechanically controlling a joint in an orthotic device, including:
(a) providing an orthotic device comprising a first strut and a second strut, wherein the first strut and the second strut are attached to a wrap spring clutch rotating about a flexion extension axis; a first orthotic member attached to the first strut a second orthotic member attached to the second strut; and
activating the clutch using electrical input signals generated by at least one contact sensor on the second orthotic member and electrical input signals generated by a kinematic sensor corresponding to the relative position and/or movement of the first and second orthotic members.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.